Endüstriyel atıkların çimento yerine ikame edilmesi ile oluşturulan beton numunelerinin mühendislik özelliklerindeki değişimin incelenmesi

Abstract

Dünya yirminci yüzyılla birlikte hızlı bir endüstriyel gelişim içerisine girmiştir. Bu gelişim medeniyet açısından büyük getiriler sağlamakla birlikte endüstriyel atıkların çevreye olumsuz etkileri göz önüne alındığında büyük sorunlar karşımıza çıkmaktadır. Bu atık malzemelerin yararlı geri dönüşüm mekanizmaları ile değerlendirilmesi maliyet açısından ve aynı zaman da çevresel etkilerin iyileştirilmesi açısından önem kazanmaktadır. Tehlikeli boyutlarda çevresel olarak sorun oluşturan inşaat sektöründe kullanımı mevcut olan atık araç lastiği, uçucu kül, silis dumanı, granüle yüksek fırın cürufu ve mermer toz atığı gibi endüstriyel atık malzemelerin, geri dönüşüm olarak değerlendirilmesi hem çevresel açıdan hem de betonun özelliklerini iyileştirmesi açısından insanlığa büyük katkılar sağlayacağı düşünülmektedir. Bu çalışmada Çanakkale Biga Bekirli Termik Santralinin uçucu külünün betonun mekanik özellikleri üzerindeki etkisi incelenmiştir. 4 farklı dayanımda beton karışımı ve kendiliğinden yerleşen beton karışımı üretilmiştir. Kendiliğinden yerleşen beton haricinde her bir beton sınıfı için şahit beton, uçucu kül içeren beton ve uçucu kül içermeyen beton üretilmiştir. Uçucu kül kullanım yüzdesi çimento miktarının % 20'si olarak alınmıştır. Uçucu kül içeren ve uçucu kül içermeyen betonlarda toplam bağlayıcı miktarının % 1'i olmak üzere kimyasal katkı kullanılmıştır. Üretimlerde 10 cm ebatlı küp kalıplar kullanılmıştır. Üretilen küp numuneler kür havuzunda 23±2 °C suda bekletilmiştir. Numunelerde 3, 7, 28 ve 56 gün sonunda basınç dayanımı testi uygulanmıştır. Yarmada çekme dayanımı testleri de yapılmıştır. Dayanıklılık testi olarak ise donma-çözünme testi gerçekleştirilmiştir. C20/25 beton karışımında orta akışkanlaştırıcı, C25/30 ve C30/37 beton karışımlarında süper akışkanlaştırıcı, C35/45 beton karışımında modifiye polikarboksilat kimyasal katkısı, kendiliğinden yerleşen beton karışımında ise polikarboksilat kimyasal katkısı kullanılmıştır. Sonuç olarak kendiliğinden yerleşen betonda uçucu kül kullanımı yaş birim ağırlık ve yayılma değerini artırmıştır. C20/25 sınıfı betonlarda uçucu kül kullanımı 3, 7 ve 56 günlük basınç dayanımlarını şahite oranla artırmış, ancak 28 günlük basınç dayanımını azaltmıştır. Uçucu kül içermeyen betonun 3 günlük basınç dayanımı şahit betonun 3 günlük basınç dayanımından daha düşüktür. C25/30 sınıfı betonlarda uçucu kül kullanılan betonların en yüksek basınç dayanımının 56. günde elde edildiği gözlenmiştir. Uçucu külün ileri ki basınç dayanımlarını artırdığı gerçeği de burada doğrulanmıştır. C30/37 ve C35/45 sınıfı betonlarda erken dayanım sonuçlarına bakıldığında uçucu külün erken dayanımları artırmadığı ileri ki dayanımları artırdığı görülmüştür. Kendiliğinden yerleşen betonda uçucu kül kullanımı 28 ve 56 günlük basınç dayanımlarını artırmıştır. Tüm beton sınıfları için ve kendiliğinden yerleşen betonlar için uçucu kül kullanımı yarmada çekme dayanımlarını artırmıştır. Farklı dayanım sınıflarındaki betonlarda ve kendiliğinden yerleşen betonda uçucu kül kullanımı donma-çözünme direncini artırmıştır.

The world has entered a rapid industrial development with the twentieth century. This development provides great returns in terms of civilization, but when considering the negative effects of industrial wastes on the environment, big problems arise. The reuse of these waste materials with useful recycling systems is important both in terms of economic and environmental impacts. It is thought that industrial wastes such as waste truck tire, fly ash, silica fume, granulated blast furnace slag and marble dust waste generally preferred in the construction industry which become dangerous to the environment are considered as recycling and will contribute to humanity in terms of improving both environmentally and concrete properties. In order to reuse waste materials in concrete and decrease production cost of conventional concrete, industrial wastes such as fly ash and blast furnace slag are replaced 20-30 percent of cement in concrete. Improving technologies should make cement production more energy efficient and environment friendly. Fly ash is a spherical granular waste material obtained from thermal power plants. Fly ash grains contain amorphous glassy crystals such as mullite, hematite, magnetite and quartz. The types of crystals that will be formed are dependent to the coal region and kiln heat. For the kilns heated with ground coal technology, 1200-1500 ºC kiln heat is generated and 1800 ºC heat is generated by the gasified coal process. With this technology, the fly ash is completely converted into fine-particle crystals and contains much higher levels of silica, alumina and iron oxide. There are two types of fly ash such as F and C types according to ASTM C 618-08 standard. The proportions for CaO, SiO and Al2O3 in the heterogeneous fly ash mixture determine the ash content. According to the American standard, 75% of the fly ash must have a particle size below 45 μm. Burning loss in fly ash should be kept at around 4%. The particle size should be well graded by applying sieve analysis. In other words, fineness is low and should be between 10-45 μm. The oxides present in the fly ash in high amounts are SiO2, Al2O3 and Fe2O3. In addition, some CaO, MgO and Na2O may be present. Fly ash is a waste material from artificial pozzolan class. There are two different groups according to the amount of CaO they contain. The first is a fly ash with a low calcareous/calcium content of less than 10% CaO, and a volatile ash with a CaO content of more than 10%. Fly ash use in concrete production was discovered in 1914 but its use began to be implemented in 1937. The pozzolanic features of volcanic tuffs similar to fly ash were first known to the Romans in the making of water canals. The burned ash from crop plants Egyptian pyramids again for the same purpose (silica pozzolan source) was used as raw material. High hydration heat emission offset is the lime component of the cement wherein the silicone by forming binder of calcium silicate hydrate and react with the fly ash particles are cemented concrete using the cement-concrete wherein a pozzolanic fly ash reduces the volume of cement needed in the concrete inside. F-type fly ash is used instead of 30-40% of the cement volume used today increases the compressive strength of the concrete structure consisting fed through pozzolan material, physical (freeze-thaw) and chemical (including the impact sulphate) improves the resistance to impact. As hydration develops, water amount is also reduced. About 60-70% of the concrete volume in cylinder-dam concretes is volatile. Pozzocrete application called preferred for this application workability of the concrete structure of the global particulate fly ash and is also facilitating the compressibility. Fly ash is also used in cement plants in the production of clinker. The silica fly core, which contains the clinker obtained as a result of combustion of clay and limestone, is also present. The use of fly ash as recycling material is an important parameter for the sustainability and raw material reserves. In USA, 22 million tons of fly ash is used in various engineering applications. This amount is up to 32% of the fly ash in thermal power plants in USA. In Europe, especially for Germany, Belgium, Netherlands and France, about 90-95% of the fly ash produced is preferred for recycling. For United Kingdom, 50% of the fly ash is used for recycling. The world's fly ash production is about 450 million tons per year. However, only 6% of this is used for cement and concrete production. Fly ash production in Turkey is about 15 million tons for one year, but fly ash use in the industry is low. According to the 1990 data, only 1% of the fly ash is used in the industry. Two reasons for low fly ash use in Turkey are considered. The first is inadequate information on fly ash properties, and the second is that there is not a uniform behaviour for fly ash. In Turkey, it is known that 15 thermic power plants produce energy with coal mines. Some of these thermic power plants are Yatağan, Kemerköy and Yeniköy in Muğla, Çayırhan in Ankara, Çan in Çanakkale, Çatalağzı in Zonguldak, Çolakoğlu in Kocaeli, Kangal in Sivas, Soma in Manisa, Orhaneli in Bursa and Sugözü thermal power plants in Adana. While stonecoal is used in Çolakoğlu and Çatalağzı power plants, imported coal is used in Sugözü and lignite coal is used in others. In Afşin-Elbistan and Manisa-Soma, C type ash with high level of lime is found according to TS 639 Turkish standard while other fly ashes are accepted as F type ash. The workability and compressive strength of concrete mixtures can be reduced when manufactured sands are substituted for naturally sourced fine aggregate. Substantial experimental studies have been investigated for concrete technology especially for high performanced concrete (properties such as compressive strength and serviceability), self-consolidating concrete, etc. Admixtures which have organic properties affected concrete properties. Superplasticisers generally improves workability and compressive strength. The chemical admixtures history began by sulphonated melamine formaldehydes in Germany and naphthalene derivatives in Japan. Then, polycarboxylate ethers were discovered. These ethers improved fluidity and resistance to segregation. For tat reason, polycarboxylate admixtures are called as new generation chemical admixtures nowadays. Some advantages of polycarboxylate chemical admixtures are reducing water-cement ratio, increasing workability retention, increasing its compressive strength and serviceability. Polycarboxylate based superplasticizers especially are preferred for self-consolidating concrete. At this experimantal study, effect of fly ash on concrete properties was investigated. Four concrete mixture which have different strength level and self-compacting concrete mixture were produced. Except for self-compacting concrete, control concrete, concrete with fly ash and concrete without fly ash were produced for each concrete class. The percentage of fly ash was 20 percent of the cement amount. In concrete containing fly ash and no fly ash, chemical admixtures was used as 1 percent of total binder amount. Cube molds of 10 cm size were preferred for placing. Cube samples were stored in water at 23 °C. Compressive strength results were found for 3, 7, 28 and 56 day specimens. In addition, split tension strength result was determined. Freezing and thawing resistance was also investigated. For C20/25 concrete mixture, mid-range plasticizer; for C25/30 and C30/37 concrete mixtures, superplasticizer; for C35/45 concrete mixture, modified polycarboxylate chemical admixture; for self-compacting concrete, polycarboxylate chemical admixture was used. Consequently, fresh unit weight and flow value of self consolidating concrete with fly ash increased. For C20/25 concrete, it was found to be significant that fly ash use increased 3, 7 and 56 day compressive strength results. However, fly ash use reduced 28 day compressive strength result. 3 day compressive strength of concrete without fly ash is less than 3 day compressive strength of control concrete. The greatest compressive strength result of concrete using fly ash in C25/30 concretes was obtained for 56 day specimens. It was significant that fly ash use increased the later compressive strength. For C30/37 and C35/45 concretes, fly ash does not increase the earlier compressive strength. However, fly ash increases the later compressive strength results. For self consolidating concrete, fly ash use increased 28 and 56 day compressive strength results. Fly ash use for all concrete classes and for self-consolidating concrete has increased split tension strength results. Fly ash use for both all concrete classses and self-consolidating concrete has increased the freezing and thawing resistance.